Synthesis And Luminescence Of Red Phosphors Based On The Rare-earth Borate Hosts

Eu³⁺ doped (Y, Gd)BO₃ has been widely used as a red phosphor for large-scale flat display panels because of its high conversion efficiency and thermodynamic stability. But (Y, Gd)BO₃:Eu³⁺ phosphor has been revealed several drawbacks such as poor color purity. Consequently, replacement solutions become necessary. Research in this way is focused on both the improvement of the existing phosphors and the development of new ones. The one aim of this work is to produce (Y, Gd)BO₃:Eu³⁺ phosphors by hydrothermal and sol-gel methods, and study their luminescence properties. The other aim is to find the new red phosphors based on the borate host and study the energy transfer process.Among the various possibilities to improve phosphors, the synthesis pathway is probably the most important. In this work, two wet chemistry methods, hydrothermal and sol-gel, are used to synthesize the (Y, Gd)BO₃:Eu³⁺ phosphors. The results show that (Y, Gd)BO₃:Eu³⁺ prepared by sol-gel process has the submicrosized and spherical shape, and its luminescent efficiency is higher than that prepared by solid state reaction, but the main emission is still orange emission. The (Y, Gd)BO₃:Eu³⁺ phosphors synthesized by hydrothermal process have different morphologies, such as rose-like, plate, spherical and fiber bundles. Compared with the commercial products, the spherical sample shows improved luminescence intensity and superior color chromaticity. With Eu³⁺ concentration increasing, the main emission peak changes from orange to red emission.As new red phosphors, Ca4GdO(BO₃)₃.Eu³⁺ and Sr₃Y₂(BO₃)₄:Eu³⁺ have the pure red emission, which is good for display application, but their luminescence efficiency is not satisfying. Their luminescence can be improved after La³⁺ and Al³⁺ co-doped. The host absorption is very important for the luminescence of phosphors. BaZr(BO₃)₂:Eu³⁺ shows good host absorption in VUV region, including the BO₃ host absorption, Ba-0 absorption band and Zr-O absorption band. Its luminescence intensity is strong but the emission is still orange, which restricts its application. Si⁴⁺ and Al³⁺ can sensitized the luminescence in the host of BaZr(BO₃)₂:Eu, but the Ti⁴⁺ and Gd³⁺ has no improvement effect, which is relation to the traps occurred in the host. After studying the luminescence of Ba_1-xEu_xB₈O₁₃ (0=x=0.2) phosphors, we find that the two luminescence centers in BaB₈O₁₃: Eu³⁺ show not only the competition emission but also the energy transfer from Eu²⁺ to Eu³⁺. As a novel phosphor, Gd₂MoB₂O₉:Eu³⁺ is synthesized by solid state reaction and its luminescence is first investigated. Under 147nm excitation, Gd_1.9Eu_0.MoB₂O₉ shows intense red emission at 626nm and its luminescence intensity is 85% than that of commercial red phosphor. The luminescent intensity of Gd₂MoB₂O₉:Eu³⁺ can be improved by doping M (M=Al³⁺, La³⁺, Y³⁺) and the Y³⁺ shows best sensitization effect.